Lecture 2 - Neuroscience Methods 2 Flashcards
What is the purpose of neuroscience techniques
Study relationship between brain and behaviour
Idea: spatial resolution cellular temporal resolution ms
Whole brain studied simultaneously = so much data difficult analyse
Non invasive
What is the spatial and temporal resolution for fmri
Spatial resolution excellent
Temporal resolution not as good as electrophysiological methods
What is an example of structural imaging
MRI
What are the goals of structural imaging
Study anatomy
Identify abnormalities
Follow development
Show plasticity
What are the structural imaging methods of interest to Biological psychology
Computed tomography CT scans
MRI - Sir Peter Mansfield
Rely on contrast between tissue types white matter vs gray matter vs cerebrospinal fluid
Example of studying juggling in structural MRI
Baseline scan
Then juggling boys practice daily until reach certain skill level
After 3 months scanned again
Example of studying juggling in structural MRI results
Scan increase grey matter in occipital region
After 3 fourth months told not to practice increase gray matter reversed
What does the study of juggling in structural MRI tell us
Brain plasticity after motor learning
Not be confused with fMRI
Correspond area hMT/V5 visual motion area
Outline the extrastriate visual areas
Process input from geniculostriate system
V5 = dorsal pathway = vision
E.g. visual coordination grasping
Supported brain structures dorsal pathway
How to generate structural MR contrast
Core: magnet generating strong EM field = external static magnetic field. Throughout and around scanner
Outsider scanner protons soft tissues all oriented at random. Undergo spinning movement in random order
Axis oriented vertical axis field. Not random
Protons spin axis generate own MF
How do protons spin axis to generate their own MF in generating structural MR contrast
Spin axis not completely vertical rotates about vertical axis
Precessional motion
More protons aligned parallel external (longitudinal) MF
Lower energy than antiparallel
How is 1 cell represented in structural MR contract
One cell represented by magnetic vector
What are important components in generating structural MR contrast
Radio frequency coils
Scanner
Outline the net magnetisation vector
Magnetisation changes in response to radio frequency pulses
Outline use of compass and a magnet in structural MR contrast generation
Compass contained surrounding fluid
Beginning points north with earths magnetic field
Magnet applied compass point east
Remove magnet and needle returns
Apply findings of use of compass and a magnet to structural MR contrast generation
Protons in bod aligned external magnetic field = net magnetisation
Radio frequency pulse applied
Net magnetisation perpendicular external magnetic field
0% inner magnetic field line with net magnetisation vector
Radio frequency pulse removed net magnetisation vector returns to original state
What is net magnetisation vector
Protons body aligned with external magnetic field
How is MR signal measured in MR contrast generation
Radio frequency pulse removed net magnetisation vector returns original state
Net magnetisation direction external magnetic field recovers 100% pre radio frequency value
MR signal measured during recovery = readout
What does the MR contrast generation draw on to produce signal
Sequences RF pulses and readout = MR protocol
Protons different tissue types gray vs white require different time realign = basis of MR contrast
What happens when you increase vertical component in MR contrast
Increase magnetisation
Protons aligned parallel with external magnetic field
That is parallel with external magnetic field
Increase longitudinal magnetisation
Spin lattice relaxation
Outline structure specific time courses of spin lattice relaxation
Brain tissue faster relaxation than ventricles CSF T1 signal
Signal brain stronger
MR contrast tissue specific
Radio frequency coil what measures T1
What creates the resulting image in specific time courses of spin lattice relaxation
Combination specific radio frequency pulse
Specific readout time
What is the order of contrasts in specific time courses of spin lattice relaxation
T1 white matter > T1 gray > T1 CSF
Outline the effects of modifying radio frequency pulses and read out times on MR properties
T2 signal white matter < gray matter < CSF
What is the goal of a functional MRI
Identify brain areas support sensory and cognitive processes
Derive models brain function
What does an fMRI measure
Blood flow
Need contrast separates non activated vs activated tissue
What are the 3 problems of fMRIs
How measure neural activity in functional contrast?
How generate measurable functional contrast in experiment?
How identify functional contrast fMRI raw data?
Outline T2 contrast underlying fMRIs for problem 1 how to measure neural activity in fMRI contrast
Depends balance deoxygenated : oxygenated haemoglobin within blood in voxel
Then depends on local regulation arterial width
Capillaries and arteries carrying blood near inactivate neutron contain both oxygen and deoxygen haemoglobin
Near active neuroma predominantly oxygenated
Outline local neuronal activation and T2 contrast problem 1 how to measure neural activity in fMRI contrast
Flow increased more oxygen capillaries
Diamagnetic = not affect local magnetic field
Deoxygenated = paramagnetic field inhomogeneous. T2 signal different oxygenated and deoxygenated blood result. Different time pause
What occurs in an inhomogeneous field during local neuronal activation in problem 1 how to measure neural activity in fMRI contrast
Horizontal magnetisation decays fasted (T2 decay)
Slower T2 decay increased MR signal
Blood oxygen dependent = BOLD effect
Outline role of BOLD signal in problem 1 how to measure neural activity in fMRI contrast
Blood oxygen level dependent
Indirect measure neural activity
Problem 2 how to generate functional stimulus related contrast
Radio frequency coil seeks excitation
Watch display on checkerboard
When stop watching and look away increase amplitude MR signal
Problem 2 how to generate functional stimulus related contrast application to an experiment
Visual cortex max BOLD signal 6 secs after visual stimuli
Temporal delay means fMRI poor temporal resolution
24 secs per trial
2% signal change time
Peak responses only 4% higher than base
Outline spaced event related design to increase signal fMRI and address Problem 2 how to generate functional stimulus related contrast
Improve contrast and noise
Design types differ in temporal sequence stimuli
Outline rapid event related design to increase signal fMRI and address Problem 2 how to generate functional stimulus related contrast
Stimuli e.g. category A and B
Immediately success each other with short diagnosis
Non correlated time cause it to become possible separate responses
Outline block design to increase signal fMRI and address Problem 2 how to generate functional stimulus related contrast
All stimuli and responses external event grouped in blocks
E.g. 20 secs baseline, 20 secs rest
Increase functional contrast:noise ratio
Responses to individual events within blocks and alert stronger signal
Outline advantages of BLOCK design
BOLD effect additive more stimuli = more signal
Good statistical power
Robust
Continuous activation
Outline disadvantages of BLOCK design
Stimuli predictable = unsuitable many tasks
Inflexible
Limited number conditions
How to address the problem of overlapping BOLD responses in Event related designs
Long stimulus intervals
Each type response unique time course - randomised ISI or randomised trial types
Advantages of Event Related Designs
Avoids habituation
Analyse subtypes responses
Disadvantages of Event Related Designs
Reduced sensitivity to neural events
Aims of experimental design for fMRI
Optimise contrast : noise Measures contrast of interest Baseline well controlled Attentional effects controlled Duration
What are the spatial pre processing steps of fMRI to identify areas that show functional contrast
Motion correction
Co-registration between subjects fMRI and anatomical scans
Normalisation: warp scans from different individuals
Spatial smoothing
Outline why the pre processing of motion correction to identify areas that show functional contrast has to occur
FMRI lasts 5-10 mins
Few subjects keep head in same position throughout
Spatial resolution 3mm movement interferes
Outline the steps or motion correct and co registration for pre processing of fMRI
Motion correction;
Align each volume of brain to target volume
Detect and correct movement
Co registration BOLD results superimposed high resolution structural image
Outline pre processing of Normalisation of fMRI
Subject 1 and 2 may have different head positions or different head shapes
Normalisation -> template -> average activation
Does motion correction help with between or within or single subjects
Single subjects
Within subject
Does normalisation help with between or within or single subjects
Between subjects
Problem with pre processing step of normalisation
Belief everyone’s brain match to 1 template
Lot variability
Caveat: sulcal variability
Outline Pre processing normalisation for comparison with anatomical template
Compare location in individual subjects
Example: location shows activation and has prior located in cordinal system
Get values for XYZ
Limitations Pre processing normalisation for comparison with anatomical template
Only 1 brain
1 hemisphere
Fixation likely changed shape brain
What data do you compare in block design
Compare signal rest with signal during blocks stimuli
Observed time course compared predicted time course = SCHEMATIC
Look voxels where predicted time course and observed time course shows good match
Disadvantages of fMRI
Low power
Type 1 errors false positives
Null results impossible interpret
Do not justify region not involved
Stat maps depend on amplitude and noise
What is phantom limb pain
Patient undergone amputation limb
Frequently reports sensation from lost limb
Can myoelecteic prosthesis prevent cortical reorganisation and phantom limb pain - Lotze et al 1999
Injury, stimulation or training induce changes homuncular organisation primary motor cortex
Change cortical periphery brain this lost limb
Phantom limb = Perceptual correlate cortical reorganisation
What happens when there is enhanced used of myoelectric prosthesis in phantom limbs
Reduced phantom limb pain
Reduced cortical reorganisation
What is the Albert Task
Patient cross out all lines on sheet paper
What are the effects of brain lesions on the Albert Task
Only crossed out lines to right half paper
What is the line bisection task
Mark bisection point middle point of each line
What are the effects of brain lesions on the Line Bisection Task
Patient chooses bisection point shifted to the right
Outline the Drawing Task
Copy picture drawing
Shown image 2 flowers asked draw
From previous experiments expect ppts only draw right hand flowed
What are the effects of brain lesions on the Drawing Task
In fact drew only the right hand half of BOTH flowers
Left remained blank
Flowers incomplete
What tasks assess brain anatomy
Albert task
Line bisection task
Drawing task
What is the goal of neuropsychology
Relate brain anatomy to behaviour
CT MRI functional localisation
Localise impaired behaviour to damaged regions - lesion May affect relay station rather originally functional region
Exclude localisation preserved skills to damaged regions. Other regions may have reorganised perform functions originally localised to damage region
Example of neuropsychology relating brain anatomy to behaviour
Association: damage single brain region but multiple deficits. Syndrome
Dissociation: damage leads impaired performance in task A bit performance Task B normal
What is an Association
Damage single brain region but multiple security
Require same neural circuit
Or
Separate functional regions are anatomical neighbours
Or
Area common relay station for anatomically functionally distinct regions
Outline the example of studying Associations Balints Syndrome
Simultanagnosia - only perceive one item at time
Deficit of perception
Oculomotor apraxia failure make eye movements
Back and forth between 2 points
Outlining perimeter
Optic ataxia - inability reach seen target
What Disorder is associated with studying dissociations
Visual form agnosia
Ventrolateral occipital lesion
What are the two tasks to test visual form of agnosia
Posting task
Perceptual matching task
Outline the posting task
Putting envelope through slot that can be rotated
Outline performance in someone with visual form agnosia in posting task
Perform reasonably well
But not good as controls
Outline the perceptual matching task
Without hand movement
Judge whether lines horizontal or vertical
Outline performance in someone with visual form agnosia in perceptual matching task
Large differences between patients and controls
Why are their apparent differences in the posting task and perceptual matching task with visual form agnosia
Difference between visual form to guide movements (posting task)
Vs visual form to recognise objects (perceptual matching task)
What brain regions can account for the differences in performance with those with visual form agnosia
Visual form guide movements: dorsal stream
Recognise objects, orientation: ventral stream
Deteriorated visual recognition and ventral stream
What is a dissociation study
Patient impaired in one task but performs normally in different task
Why does the interference occur in dissociation task
Impaired task more difficult?
Performance unimpaired task at ceiling?
Outline visual agnosia patients performance in discriminating shapes visually
Poor
Failed complete objects outline
Inability recognise line drawings or shapes
Outline visual agnosia patients performance in grasping irregularly shaped objects
Good
Outline optic ataxia patients performance in discriminating shapes visually
Good
Outline optic ataxia patients performance in grasping irregularly shaped objects
Poor
Unable use visual info about object shape to control movement
Difficulty pointing or grasping movements
Symptom Balints Syndrome
Why does Goodale et al 199 believe there are differences in optic ataxia and visual agnosia patients
Different brain circuits for visual perception vs visual control of skilled action
What are the effects of visual pathway lesions to ventral stream
Poor visual shape discrimination
Good visually guided movement
What are the effects of lesions to dorsal stream
Good visual shape discrimination
Poor visually guided movements
Outline step 1 for measuring double dissociation for right frontal lobe lesions impairing memory for designs vs words
1st compare same right frontal region with controls
Right frontal lesion poorer performance memory designs
Double dissociation - compare controls right and left frontal lesions
Double dissociation for right frontal lobe lesions impairing memory for designs vs words findings
Left frontal lesion worse for memory words
Non overlapping component operations
Poor memory designs due to unspecific attention deficit
Outline limitation that variation in pathologies makes group studies difficult
Inference from single patients weak Lesion size and location variable Hard find similar patients Normalisation scans weakens anatomical inference Functional anatomy variable
Outline effects of lesion size on behavioural outcome
Small lesions = little effects. Robust partial damage
Small lesions strategic locations = deficit
Large lesions = damage several centres
Reorganisation: intact regions change behaviour
How can limitations be overcome
Combining different methods with complementary strengths
